Question

)State how viscosity and modulus change upon curing a thermosetting resin. ( 4 pt)

Answer 1

Curing is the final stage(after mixing, blending, extrusion) which extensively decides the visco-elastic behavior of the polymers. There is a set curing temperature at which a polymer gains its chemical and mechanical properties after the processing.

The molecular mobility during curing reactions at curing temperature highly influences the viscosity and modulus of the polymer at the end.

In polymer characteristics, there is a term called response time which tells us how the curing temperature and curing duration have an influence on the cured product based on how much elasticity it shows.

The gel point decides the modulus of the polymer. The polymer can only gain its ultimate strength after the curing temperature has crossed the gelling stage.

In a typical cure cycle for a thermosetting resin or composite, there are various stages of viscosity change within the polymer.

• Viscous( Before gelation)
• Rubbery( After Gelation)
• Glassy solid( At the end due to vitrification)

The variation in modulus takes a transition from maxima to minima. This happens due to phase transition from rubbery to a glassy structure after curing. It depends on the induced strength due to vitrification.